Domestic battery master switch

[Dank]

Hi

 

I am just in the process of rewiring my batteries (the builder has installed brown & blue cables)and making up new leads when I noticed that the domestic battery feed from the engine runs into the master switch and then on to the battery positive link with a lead from the battery to the trip panel. To my mind this set up means that if the master switch is removed the battery will not charge but the batteries will still feed the trip panel.

I'm thinking that the lead from the engine should go to the positive side of the battery, then onto the master switch and on to the trip panel bus bar. This will issolate the battery from the trips but will leave it permanently wired to the alternator. Hope I've not made things too confusing.

Am I right or just chasing my tail?

 

David

[Pretty Funked Up]

From your description it sounds like the isolator will isolate the alternator. Really not a good thing if the engine is running.

 

It sounds very odd that it would leave the feed going to the fuse panel, are you sure?

its an easy test (with the engine off)

[GUMPY]

Hi

 

I am just in the process of rewiring my batteries (the builder has installed brown & blue cables)and making up new leads when I noticed that the domestic battery feed from the engine runs into the master switch and then on to the battery positive link with a lead from the battery to the trip panel. To my mind this set up means that if the master switch is removed the battery will not charge but the batteries will still feed the trip panel.

I'm thinking that the lead from the engine should go to the positive side of the battery, then onto the master switch and on to the trip panel bus bar. This will issolate the battery from the trips but will leave it permanently wired to the alternator. Hope I've not made things too confusing.

Am I right or just chasing my tail?

 

Ignoring he colours the switch is wired correctly to meet the BSS

However mine and many others are wired directly from the alterntor to the battery.

[WotEver]

Hi

 

I am just in the process of rewiring my batteries (the builder has installed brown & blue cables)and making up new leads when I noticed that the domestic battery feed from the engine runs into the master switch and then on to the battery positive link with a lead from the battery to the trip panel. To my mind this set up means that if the master switch is removed the battery will not charge but the batteries will still feed the trip panel.

I'm thinking that the lead from the engine should go to the positive side of the battery, then onto the master switch and on to the trip panel bus bar. This will issolate the battery from the trips but will leave it permanently wired to the alternator. Hope I've not made things too confusing.

Am I right or just chasing my tail?

 

David

Hi David,

 

To fully comply with the BSS, one side of the switch should have the +ve feed from the domestic batteries. The other side of the switch should have everything else - alternator, fusebox etc.

 

The point Idleness is making is that the alternative is to move the alternator cable to a permanent connection on the battery +ve. Many (possibly most) boats are wired like this and it'd take a particularly sharp inspector to notice.

 

While you're wiring them up, have you studied this page of Gibbo's?

 

Cheers,

Tony

[steelaway]

Hi

 

I am just in the process of rewiring my batteries (the builder has installed brown & blue cables)and making up new leads when I noticed that the domestic battery feed from the engine runs into the master switch and then on to the battery positive link with a lead from the battery to the trip panel. To my mind this set up means that if the master switch is removed the battery will not charge but the batteries will still feed the trip panel.

I'm thinking that the lead from the engine should go to the positive side of the battery, then onto the master switch and on to the trip panel bus bar. This will issolate the battery from the trips but will leave it permanently wired to the alternator. Hope I've not made things too confusing.

Am I right or just chasing my tail?

 

David

 

 

 

I would always have the alternator wire connected directly to the battery's - the switch is only to isolate the battery power to the boat.

Any other way would risk damaging the alternators.

 

Alex

[WotEver]

I would always have the alternator wire connected directly to the battery's...

Me too. However, it contravenes the BSS.

 

Tony

[Dank]

Thanks gents.

 

This all confirms my belief that the battery switch is in the wrong position, another builder cockup. Batteries being rewired in red and black and will tie alternator feed into batt +ve but with a little slack so it can be swung onto the master switch if examiner were to object.

 

David

[Tim F]

3.6.2 all electric circuits must pass through a battery isolator blah blah blah.

[Pretty Funked Up]

3.6.2 all electric circuits must pass through a battery isolator blah blah blah.

 

Isnt most common to have the alternator charge piggy back the starter motor cable?

a short link from alternator to starter motor, then massive cable back to the starter battery.

 

or are dual alternator setups the most common these days?

 

also pretty sure it goes on to say that not all circuits have to pass through the isolator but other circuits such as bilge pump need to be suitably fused.

Edited October 23, 2011 by Pretty Funked Up

[davidc]

3.6.2 all electric circuits must pass through a battery isolator blah blah blah.

 

I would argue that it refers to all circuits after the battery, all circuits before apply to the alternator circuit, which is part of the engine supplying the battery.

[WotEver]

I would argue that it refers to all circuits after the battery, all circuits before apply to the alternator circuit, which is part of the engine supplying the battery.

It does allow for certain specific exceptions such as bilge pump, alarm, charger etc. However alternator is not one of the exceptions.

 

Tony

 

... will tie alternator feed into batt +ve but with a little slack so it can be swung onto the master switch if examiner were to object.

The perfect solution

[Pretty Funked Up]

It does allow for certain specific exceptions such as bilge pump, alarm, charger etc. However alternator is not one of the exceptions.

 

Tony

 

surely theres a BSS chap who can say if the alt. needs to be isolated by the isolator?

If so, any dates on the rule?

 

I have enough slack to change it also if it needs to be done.

 

HANG ON: I already know the answer. Theres nothing within the rules to say you cant isolate on the negative! ergo no isolator needed for the alternator

Edited October 23, 2011 by Pretty Funked Up

[davidc]

It does allow for certain specific exceptions such as bilge pump, alarm, charger etc. However alternator is not one of the exceptions.

 

Tony

 

 

The perfect solution

 

 

If you read it it always talks about battery to etc, the alternator is to battery

Example 3.2.2

 

 

Check the size of the following cables.

battery to master switch;

battery or master switch to starter solenoid;

battery to battery;

engine return to battery or master switch;

battery to bow-thruster motor;

battery to anchor winch motor;

battery to inverter system (over 1000w size).

The battery cables prescribed in the check must be

approximately 25mm2.

 

3.6.2

Certain circuits supplying power to equipment that requires a

continuous supply, e.g. bilge pump, may bypass the battery isolation

switch. However, the risks associated with a short circuit or

overload fault must be minimised particularly when the boat is

left unattended.

 

Again the battery does not supple power to the alternator

 

but that is my opinion

[AJLintern]

Why not just have the starter motor battery feed also passing through the same isolation switch - when switched off you can't start the engine anyway, so no damage to the alternators

[WotEver]

surely theres a BSS chap who can say if the alt. needs to be isolated by the isolator?

I'm pretty sure that Rob has already answered this one although the stupid search facility isn't proving any help in finding it for me.

 

There's no doubt that it isn't allowed to have the Alt permanently connected but there's equally no doubt that an awful lot of boats do have it permanently connected.

 

Tony

 

If you read it it always talks about battery to etc, the alternator is to battery <snip> the battery does not supple power to the alternator

Let's see you play that game of syntax with a sharp-eyed BSS inspector who's just about to fail your boat

 

Why not just have the starter motor battery feed also passing through the same isolation switch...

Because that would join the batteries together, wouldn't it?

 

What you can do, and many boats are wired in this way, is to power the solenoid from the domestics. Which achieves the same objective - isolator off, no starty engine.

[AJLintern]

Because that would join the batteries together, wouldn't it?

Not with a double pole switch it wouldn't But yes driving the solenoid via the domestic batteries is another neat alternative!

[davidc]

I'm pretty sure that Rob has already answered this one although the stupid search facility isn't proving any help in finding it for me.

 

There's no doubt that it isn't allowed to have the Alt permanently connected but there's equally no doubt that an awful lot of boats do have it permanently connected.

 

Tony

 

 

Let's see you play that game of syntax with a sharp-eyed BSS inspector who's just about to fail your boat

 

 

 

 

 

 

 

One of my rules of life never argue with people who can really screw you up

i.e

Police

Mot inspectors/bss inspectors

Tax inspectors

 

But back to subject here is link which explains it well

 

http://www.smartgauge.co.uk/alt_how.html

[ditchcrawler]

Ignoring he colours the switch is wired correctly to meet the BSS

However mine and many others are wired directly from the alterntor to the battery.

Welcome home

[steelaway]

I would argue that it refers to all circuits after the battery, all circuits before apply to the alternator circuit, which is part of the engine supplying the battery.

 

 

 

Indeed

 

Alex

[Chalky]

Me too. However, it contravenes the BSS.

 

Tony

 

That's exactly how mine is wired as well. If you're changing the wiring think about adding a fuse in between the battery and the switch. If there's a catastrophic short in the system it's your last line of defence. I've got a 250A in the domestic and a 400A in the engine circuits. Mount them outside the battery box so they don't ignite any hydrogen in there when they let go.

[GUMPY]

Welcome home

Thanks I wont mention how crap a certain airline are and how we spent 6 hours at the airport with only a 5euro food voucher each..........

 

 

Back on topic

Mine is wired so that there is a loop of cable that will reach both the switch and the battery, strangely it moves from one to the other and back again every 4 years.

Reminds me I must get a new BSS before my licence is due in January

Edited October 23, 2011 by idleness

[Tim F]

If the isoator is between the alt and batteries then none of the electrical circuits can be isolated. The only two places to fit one are on the positive lead between battery and distribution panel or on the low resistance return cable from the engine or starter motor to the battery. That will pass any BSS exam.

[WotEver]

If the isoator is between the alt and batteries then none of the electrical circuits can be isolated.

????

 

Would you care to explain your thinking? That's exactly how the BSS staes it SHOULD be wired - Batteries on one side, Alt & everything else on the other.

 

Tony

[by'eck]

I would always have the alternator wire connected directly to the battery's - the switch is only to isolate the battery power to the boat.

Any other way would risk damaging the alternators.

 

Alex

 

Fair comment but IMHO a battery isolator should do just that, completely isolate the battery irrespective of what the BSS says. I don't like nasty surprises when changing batteries or working on the engine with a live alternator.

 

If you really think there is a chance you might forget to turn it on before starting engine, arrange it to disable starter when off.

[AJLintern]

Would also have to make sure the fuel cut off solenoid activates when the master switch is turned off, thus stopping the engine if it's already running.